Preliminary Study Of Core Tungsten Concentration In CFETR With Full Tungsten Wall

In order to maintain the high-power steady-state operation of the fusion reactor,it is necessary to limit the impurity concentration in the core.For high Z materials,the concentration allowed in the core is lower because of its high radiation energy.However,due to the high corrosion rate and tritium retention of low Z materials,we have to consider the use of high Z materials as plasma facing materials.For high Z plasma facing materials,W is the best choice because it has the highest binding energy and is therefore more difficult to be sputtered.On the other hand,due to the engineering restrictions,we need to limit the reach of energy flux onto the divertor.Puffing medium Z particles into the plasma in the peripheral can effectively reduce the radiation energy and energy flux onto the divertor target.However,these charged impurities will further sputter the W impurities by impinging on the wall material,and then affect the concentration of W ions.For China fusion engineering test reactor（CFETR）,the simulation study of the sputtering of W target plate has been carried out for the condition of the impurity gas puffing,but the simulation for the whole tungsten wall has not been performed.In this paper,for the lower single-null divertor configuration,SOLPS and DIVIMP software are used to simulate the erosion and transport of W in the condition of full W wall CFETR under different Ne injection rates.In order to understand the influence of the main chamber wall,the tungsten sputtering flux is estimated by extrapolation of the plasma parameters at the outmost mesh for SOLPS in the manner of exponential decay.The simulation results show that increasing puffing rate can effectively reduce the impurity concentration of W,only considering the sputtering of the target,when the injection rate reached 2.1×10²¹s^-1,the concentration of W in the core is already below the level of 10^-5.However,the concentration of W in the core increases to 10^-4 when taking sputtering on the wall into account,and it does not decrease obviously with the increase of puffing rate.Therefore,more attention should be paid to the sputtering of main chamber wall in the future.